1. Field of the Invention
The present invention relates to a method used in a wireless communications system and related communication device, and more particularly, to a method of performing uplink transmission in a wireless communication system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as to user equipments (UEs).
In the LTE system, a user equipment (UE) may perform measurement to measure communication quality, such as quality of a frequency layer or strength of a radio signal, which is controlled by the E-UTRAN, due to mobility of the UE. Measurement can be divided into two types according to the current operating frequency of the UE, which are an intra-frequency measurement and an inter-frequency/inter-RAT measurement. The intra-frequency measurement is predominantly performed for the mobility within the same frequency layer (i.e. between cells with the same carrier frequency), whereas the inter-frequency/inter-RAT measurement is predominantly performed for the mobility between different frequency layers (i.e. between cells with a different carrier frequency). In addition, the inter-frequency/inter-RAT measurement is performed during uplink/downlink idle periods, such as a measurement gap configured by the network. During the measurement gap, both the uplink and downlink transmissions are prohibited, and thereby the inter-frequency/inter-RAT measurement can be performed within the measurement gap.
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at a cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), UL multiple-input multiple-output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-A system by which two or more component carriers are aggregated to achieve a wider-band transmission. Accordingly, the LTE-A system can support a wider bandwidth up to 100 MHz by aggregating a maximum number of 5 component carriers, where bandwidth of each component carrier is 20 MHz and is backward compatible with 3GPP Rel-8. An LTE-A specification supports carrier aggregation for both continuous and non-continuous component carriers with each component carrier limited to a maximum of 110 resource blocks. The carrier aggregation increases a bandwidth flexibility by aggregating the non-continuous component carriers. A component carrier is used as an UL component carrier or a downlink (DL) component carrier. Further, there is a one-to-one correspondence between the UL component carrier and the DL component carrier, i.e., each UL component carrier is paired with a corresponding DL component carrier. In an LTE-A time-division duplex (TDD) system, the UL component carrier and DL component carrier are the same component carrier.
When the UE is configured with the carrier aggregation (CA), the UE is allowed to receive and transmit data on one or multiple component carriers to increase the data rate. In the LTE-A system, it is possible for the eNB to configure the UE different numbers of UL and DL component carriers which depend on UL and DL aggregation capabilities, respectively. Moreover, the component carriers configured to the UE necessarily consists of one DL primary component carrier (PCC) and one UL primary component carrier. Component carriers other than the primary component carriers are named UL or DL secondary component carriers (SCCs). The numbers of UL and DL secondary component carriers are arbitrary, and are related to the UE capability and available radio resource. The UL and DL primary component carriers are used for establishing and re-establishing the radio resource control (RRC), and transmitting and receiving the system information. The UL or DL primary component carrier can not be de-activated, but can be changed by a handover procedure with the RACH procedure. However, component carriers on which the UE can perform the RACH procedure have not been known and the process of changing UL or DL primary component carrier can not be completed without performing the RACH procedure.
According to the specification released by 3rd Generation Partnership Project (3GPP), if the UE receives both a grant in a Random Access Response and a grant for its Cell Radio Network Temporary Identifier (C-RNTI) or Semi persistent scheduling (SPS) C-RNTI requiring transmissions in the same UL subframe (i.e. transmission time interval (TTI)), the UE may choose to continue with either the grant for its RA-RNTI or the grant for its C-RNTI or Semi persistent scheduling C-RNTI.
However, if the UE is configured with a primary component carrier and at least one secondary component carrier (i.e. corresponding to a PCell and at least a SCell, respectively), the UE may receive a first uplink grant on a PDCCH for a secondary component carrier during a random access procedure on the primary component carrier and receive a second uplink grant in a Random Access Response message for transmissions in a same subframe. Under such a situation, the UE either chooses the first uplink grant on PDCCH or the second uplink grant in the Random Access Response message for transmission in the subframe, which is not efficient since only one transmission is allowed while the first uplink grant and the second uplink grant are for different component carriers, i.e. the secondary component carrier and the primary component carrier respectively.
On the other hand, according to the specification released by 3GPP, when a configured uplink grant (i.e. an SPS grant) is indicated during a measurement gap and indicates an UL-SCH transmission during a measurement gap, the UE processes the configured grant but does not transmit on an Uplink Shared Channel (UL-SCH), i.e. processing the SPS grant for transmission information but not transmitting corresponding data.
However, if the UE is configured with a primary component carrier and at least one secondary component carrier (i.e. corresponding to a PCell and at least a SCell, respectively), the UE may have a measurement gap configuration for a secondary component carrier and a configured uplink grant indicating an UL-SCH transmission during the measurement gap for the primary component carrier since the UE may have different measurement gap configurations for different component carriers. Under such a situation, the UE does not perform the UL-SCH transmission. No transmission wastes the configured uplink grant resources since the measurement gap and the configured uplink grant occupy different frequency resources.